Exclude final methods when checking dyn-compatibility

Author: mu001999

compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs

@@ -314,6 +314,11 @@ pub fn dyn_compatibility_violations_for_assoc_item(
     trait_def_id: DefId,
     item: ty::AssocItem,
 ) -> Vec<DynCompatibilityViolation> {
+    // `final` assoc functions don't prevent a trait from being dyn-compatible
+    if tcx.defaultness(item.def_id).is_final() {
+        return Vec::new();
+    }
+
     // Any item that has a `Self: Sized` requisite is otherwise exempt from the regulations.
     if tcx.generics_require_sized_self(item.def_id) {
         return Vec::new();

tests/ui/traits/final/dyn-compat.rs

@@ -0,0 +1,24 @@
+//@ check-pass
+
+#![feature(final_associated_functions)]
+
+trait Foo {
+    final fn bar<T: std::fmt::Debug>(&self, t: T) {
+        println!("{:?}", t);
+    }
+
+    fn baz(&self) {}
+}
+
+impl Foo for () {}
+impl Foo for i32 {}
+
+fn foo(x: &dyn Foo) {
+    x.bar(42);
+    x.baz();
+}
+
+fn main() {
+    foo(&());
+    foo(&42);
+}